unit 1.4

Question 1

Metabolism?

Answer 1

all the organisms chemical processes, comprising anabolic and catabolic pathways

Question 2

Metabolic Pathways?

Answer 2

a sequence of enzyme controlled reactions in which a product of 1 reaction is a reactant in the next

Question 3

What does Metabolism refer to?

Answer 3

all of the reactions of the body
Reactions occur in sequences called metabolic pathways

Question 4

Anabolic reactions?

Answer 4

building up molecules e.g
protein synthesis

Question 5

Catabolic reactions?

Answer 5

breaking molecules down e.g digestion

Question 6

what are metabolic pathways controlled by?

Answer 6

enzymes
the products of 1 enzyme controlled reaction becomes reactants in the next

Question 7

What are enzymes?

Answer 7

a biological catalyst, a protein made by cells that alters the rate of chemcal reaction wihtout being used up by the reaction

Question 8

What are catalysts?

Answer 8

an atom that alters the rate of chemical reaction without taking part in the reaction or being changed by it

Question 9

What properties do enzymes and chemical catalysts share

Answer 9

They speed up reactions
not used up
not changed
have a high turn over number i.e they catalyse many reactions per second

Question 10

What reactions do enzymes catalyse?

Answer 10

reactions that are energetically favourable and would happen anyway
without enzymes, reaction in cells would be too slow to be compatible with life

Question 11

Structure of enzymes?

Answer 11

proteins with a tertiary structure and the protein folds into a spherical globular shape with hydrophilic R groups on the outside of the molecule, making enzymes soluble.
Each Enzyme has a particular sequence of amino acids and the elements in the R groups determine the bonds make with each other
These are H bonds, disulphide bridges and ionic bonds and they hold the enzymes molecules in its tertiary form.
small area with a specific 3d shape = active site which gives enzyme many of its properties

Question 12

Where are enzymes made?

Answer 12

inside cells
3 distinct sites where they act
extracellular
intracellular ( in solution)
intracellular ( membrane bound)

Question 13

Extracellular?

Answer 13

some enzymes = secreted from cells by exocytosis and catalyse extracellular reactions.
Amylase - made in the salivary glands moves down the salivary ducts to the mouth.
Saprotrophic fungi + bacteria secrete amylases, lipases and proteases onto their food. which digest it and the organisms absorb the products of digestion

Question 14

Intracellular in solution?

Answer 14

Intracellular enzymes act in solution inside cells e.g enzymes catalyse glucose breakdown in glycolysis
enzymes in solution in the stroma of chloroplasts catalyse the synthesis

Question 15

Intracellular membrane bound?

Answer 15

Intracellular enzymes may be attached to membranes e.g on the cristae of mitochondria where they transfer electrons and H ions in the ATP formation

Question 16

Active site?

Answer 16

the specific 3 dimensional site on an enzyme molecule to which the substrate binds by weak chemical bonds

Question 17

Enzyme substrate complex?

Answer 17

intermediate structure formed during an enzyme - catalysed reaction in which the substrate ad enzyme bind temporarily, such that the substrates are close enough to react

Question 18

What is the Lock and key model?

Answer 18

where the unique shape of the active site means that an enzyme can only catalyse one type of reaction.
Other molecules with different shapes wont fit
substrate is imagined fitting into the active site as a key fits into a lock. Shapes of lock and key = specific to one another

Question 19

Enzyme specificity?

Answer 19

that an enzyme is specific for its substrate

Question 20

Induced fit?

Answer 20

the change in shape of the active site of an enzyme induced by the entry of the substrate, so the enzyme and substrate bind closely

Question 21

Why was the induced fit theory proposed?

Answer 21

as enzymes shape was altered by binding its substrate suggested that it is not as rigid as originally thought.
Induced fit - proposed to suggest the enzyme shape slightly accommodated the substrate

Question 22

Active site?

Answer 22

the minimum energy that must be put into a chemical system for a reaction to occur

Question 23

Why do molecules need kinetic energy?

Answer 23

for them to approach each other closely enough to react

Question 24

One way of making chemicals react?

Answer 24

to increase their kinetic energy, to make successful collisions between them more likely

Question 25

How do we do this?

Answer 25

with heat
as heat speeds up reactions in non living systems but in most living organisms, temps above 40 degrees cause irreversible danature to proteins and they denature

Question 26

How do they combat this?

Answer 26

enzymes work by modifying the substrate so the reaction requires a lower activation energy.
when a substrate enters the active site of an enzyme, the shape of the molecule alters, allowing reactions to occur at lower temps i.e with lower kinetic energy than in the absence of enzymes

Question 27

What does the graph for an enzyme controlled reaction mean?

Answer 27

When the enzyme and substrate are first mixed together, there are many substrate molecules
Both enzyme and substrate molecules are in constant motion and collide
Substrate molecules bind to the active site of the enzyme molecules. In a successful collision, substrate = broken down and products are released.
More active sites - become filled with substrate molecules
Initially, the rate of reaction depends on the number of free active sites. If all other conditions = optimal and thtere is excess substrate. The enzyme conc = limiting factor because it controls the rate of the reaction.
As the reaction proceeds there is less substrate and more product.
the enzyme concentration is constant. The substrate concentration and is the limiting factor because it controls the rate of reaction.
Eventually, all the substrate has been used and no more product can be formed so the line plateaus
Line goes through the origin, because at 0 time, no reaction has happened yet.

Question 28

Denaturation?

Answer 28

the permanent damage to the structure and shape of a protein molecule e.g an enzyme molecule due to for example high temp or extreme pH

Question 29

Inactivation?

Answer 29

reversible reduction of enzyme activity at low temp as molecules have insufficient kinetic energy to form enzyme substrate complexes

Question 30

How environmental conditions affect enzyme activity?

Answer 30

they change the 3D structure of enzyme molecules. Bonds= broken and configuration of the active site is altered, changing the rate of reaction.
The concentrations of enzyme and substrate also affect the rate of reaction by changing the number of enzyme - substrate complexes formed

Question 31

Effect of temp on enzyme action?

Answer 31

increased temp, increases kinetic energy of the enzyme and substrate molecules and they collide with enough energy more often, increasing the rate of reaction.
The rate of reaction doubles foreach 10 degrees rise in temp up to a particular temp, about 40 degrees for most enzymes.
Above this temp, molecules have more KE but reaction rate goes down because their increasing vibration breaks H bonds, changing the tertiary structure
Alters the shape of the active site and the substrate will not fit.
Enzyme = denatured, permanent change in structure
At low temps, enzyme =inactivated as the molecules have very low Kinetic energy. However shape = unchanged and the enzyme will work again if the temp is raised.

Question 32

Effect of pH on enzyme action?

Answer 32

most enzymes have an optimum pH, at which the rate of reaction is highest. Small pH changes around he optimum cause small reversible changes in enzyme structure ad reduce its activity but extremes of pH denature enzymes.
Charges on the amino acid side - chains of the enzymes’ active site = affected by H ions or OH ions
at low pH, excess H+ ions are attracted to negative charges and neutralise them.
At high pH excess OH- ions neutralise the positive charges.
This disrupts the ionic and H bonds maintaining the shape of the active site.
The shape changes denaturing the enzyme.
No enzyme - substrate complexes form and enzyme activity is lost.

Question 33

Substrate concentration?

Answer 33

the rate of an enzyme-catalysed reaction varies with changes in substrate concentration.
If the enzyme conc = constant, the rate of reaction increases, as the substrate concentration increases.
At low substrate concentrations, the enzyme molecules have only a few substrate molecules to collide with, so the active sites are not working to full capacity.
With more substrate, the more active sites = filled. The concentrations of substrate is controlling the rate of reaction and so is a limiting factor.
As even more substrate = added, at a critical conc, all the active sites become occupied and the rate of reaction is at its max
when all the active sites = full, the enzyme us said it be saturated.

Question 34

What happens when more substrate is added?

Answer 34

reactions cannot be catalysed any faster and so the line plateaus.
The substrate conc is no longer controlling the rate of reaction so it is no longer a limiting factor

Question 35

Limiting factor?

Answer 35

a factor that when in short supply limits the rate of a reaction.
An increase in the value of a limiting factor causes an increase in the rate of reaction

Question 36

Enzyme concentration on enzyme activity?

Answer 36

once a product leaves the active site, the enzyme molecule can be reused, so only a low enzyme concentration is needed to catalyse a large number of reactions.
One of the fastest acting enzymes = catalase has a run over number of 40 million molecules per second.
It breaks down the tightly toxic waste hydrogen peroxide.
as the enzyme conc increases, there are more active sites available and therefore rate of reaction increases.

Question 37

The turn over number?

Answer 37

The number of substrate molecules that one enzyme can turn into products in a given number

Question 38

Inhibitor?

Answer 38

a molecule or ion hat binds to an enzyme and reduces the rate of reaction, the enzyme catalyses

Question 39

Competitive inhibition?

Answer 39

Reduction of the rate of an enzyme - controlled reaction by a molecule or ion that has a complementary shape to the active site, similar to the substrate and binds to the active site, preventing the substrate from binding.

Question 40

Enzyme inhibition?

Answer 40

the decrease in rate of an enzyme controlled action by another molecule, an inhibitor.
An inhibitor combines with an enzyme and prevents it forming an enzyme substrate complex.

Question 41

competitive inhibitors?

Answer 41

have a molecular shape complementary to the active site and similar to that of a substrate, so they compete for the active site e.g in the mitochondrial matrix.

Question 42

For example?

Answer 42

Malonic acid has a similar shape to succinic acid so they compete for the active site of succinic dehydrogenase.
Increasing the concentration of the substrate, succinic acid reduces the effect of the inhibitor, because the more substrate molecules present, the greater the chance of binding to active sites leaving fewer available for the inhibitors.
But if the inhibitor concentration increases, it binds to more active sites and so the reaction rate == slower.

Question 43

Non competitive inhibitors?

Answer 43

An atom, molecule or ion that reduces the rate of an enzyme controlled reaction by binding to the enzyme at position other than the active site, altering the shape of the active site and preventing the substrate from successfully binding to it.

Question 43

How does it work?

Answer 43

they bind to the enzyme at an allosteric site, so they do not compete with the substrate.
They affect bonds within the enzyme molecule and its overall shape, including that f the active site.
The substrate cannot bind with the active site and so no enzyme substrate complexes form.
As the inhibitor conc increases, the rate of reaction and the final mass of product decrease
Examples include Pb2+ and Ar2+

Question 44

allosteric site?

Answer 44

a site other than the active site

Question 45

Immobilised enzyme?

Answer 45

Enzyme molecules bound to an inert material over which the substrate molecules above

Question 46

What are they?

Answer 46

enzymes when they are fixed, bound or trapped on an inert matrix e.g sodium alginate beads or cellulose microfibrils.
These can be packed into glass columns. Substrate is added to the top of the column and as it flows down, its molecules bind to the enzyme molecules’ active site, both on the bead surface and inside the beads as the substrate molecules diffuse in.
once set up, the column can be used repeatedly
the enzyme = fixed and does not contaminate the products.
Products are therefore easy to purify.
Immobilised enzymes = used widely in industrial processes such as fermentation as they can be easily recovered forreuse

Question 47

Why are immobilised enzymes good?

Answer 47

Immobilising enzymes make enzymes more stable because it creates a microenvironment, allowing reactions to occur at a higher temp or more extreme pHs more normal/
Trapping an enzyme molecule prevents the shape change that would denature its active site, so the enzyme can be used in a wider range of physical conditions than if it were free in solution.

Question 48

Why do immobilised enzymes in beads have a lower rate of reaction than them in a membrane?

Answer 48

Because some of the active sites are inside the beads and the substrate takes time to diffuse to them.
Enzymes on a membrane are readily available for binding so give a higher reaction rate.

Question 49

Advantages of immobilised enzymes?

Answer 49

increases stability and function over a wide range of temp and pH than enzymes free in solution
Products = not contaminated with the enzyme
Enzymes = are easily recovered for reuse
A sequence of columns can be used so several enzymes with differing pH or temp optima can be used in one process
Enzymes can be easily added or removed, giving a greater control over the reaction

Question 50

Uses of immobilised enzymes?

Answer 50

Lactose free milk
biosensors

Question 51

lactose free milk?

Answer 51

The milk is passed down a column containing immobilized lactose
the lactose binds to the active sites on the lactase and is hydrolysed into its components, glucose + galactose

Question 52

Biosensors?

Answer 52

they rapidly and accurately detect, identify and measure even very low concentrations of important molecules.
They work on the principle that enzymes = specific and are able to select one type of molecule from a mixture, even at very low concentrations.
One use is in the detection of blood glucose.
The enzyme glucose oxidase, immobilised on a selectively permeable membrane is placed in a blood sample, binds glucose.
provides a small electrical current, detected by the electrode and read on a screen.
Enzymes can also be immobilised onto test strips, where different strips may detect a variety of molecules.
Testing strips with glucose oxidase immobilised onto them are used for detecting glucose in urine

Question 53

HFCS?

Answer 53

high fructose
corn
syrup
where HFCS is manufactured in a multi step process from starch.
Uses several immobilised enzymes requiring different physical conditions
include
starch — oligosaccharides –glucose – fructose